1. Field of the Invention
The present invention relates, generally, to solar energy receiver devices and, more particularly, to solar energy receiver systems utilizing stretched membranes. Specifically, the present invention relates to an improved support and tracking apparatus for stretched membrane solar energy concentrators which reflect the incident solar energy to a receiver mechanism.
2. Description of the Prior Art
In general, conventional solar energy receiver or collector structures are relatively large, having concentrator mirror diameters in the range of to 3-15 meters. The mounting arrangement for supporting such solar concentrators as well as the drive mechanism for steering or maneuvering the concentrators is usually of considerable size and mass. For example, in order for a more conventional, bulkier dish support structure to withstand excessive wind forces, a central pedestal for the drive mechanism and the mirror receiver normally includes a massive metal post to avoid buckling and a massive concrete foundation to prevent uprooting or overturning. In addition, the maneuvering of the solar receiver usually requires costly support shaft bearings and gear drive motors. The production and installation costs for these drive mechanism, pedestals, and foundations represent a large portion of a total cost of central receiver solar power systems that utilize dishes or heliostats. Such costs are a substantial factor in determining the feasibility of utilizing and maintaining such systems. An example of such a complicated and massive structure is illustrated in the solar concentrator system disclosed in U.S. Pat. No. 3,872,854. In addition, a parabolic mirror device utilized as a heating apparatus is also disclosed in U.S. Pat. No. 4,249,515.
More recently, in an attempt to reduce the material, fabrication, and maintenance costs of solar concentrators and their allied structures, solar concentrator mirrors or reflectors have been formed from stretched membranes of polymeric or metallic material. The reflector module usually includes a rim or frame to which a stretched membrane is attached. For optical accuracy, it is necessary that the shape of the frame on which the membrane is attached be rigidly maintained.
One known method of providing support and drive capability for stretched-membrane heliostats and mirrors is through the use of a support spider. The support spider is constructed of cantilevered trusses having first ends attached to the rim of the stretched membranes and opposite ends converging to a junction zone that connects to a drive and support arrangement. However, the connection of a support spider to the rim of the heliostat mirror and to the drive mechanism support pedestal is typically an intricate arrangement that also requires the use of costly support shafts, bearings, and gear drive motors. Moreover, cantilevered structures are not as efficient as either tension structures or well designed compressive structures.
Up to the present time, research efforts have focused on developing the stretched membrane reflector concept and have demonstrated very large reductions in cost and weight for membrane concentrator reflector modules. However, such efforts have typically taken these resultant efficient and low cost reflector modules and integrated them with conventional and expensive support and tracking structures. For example, by placing the stretched membrane module on a conventional center articulated spider truss frame subsystem, which is typical for both dish and heliostat concepts, much of the advantage of stretched membrane reflectors has not been realized. Accordingly, the entire concentrator must be configured as a system to arrive at an optimum design for the stretched membrane concentrator. As the result, there is still a need for support and maneuvering systems for solar energy receivers, and particularly stretched membrane concentrators, which systems are efficient, effective and strong and yet inexpensive to construct and operate.